The invention disclosed herein relates generally to mechanisms which respond to successive actuations by assuming alternate states, and more particularly to low travel, high tactile feedback push button mechanisms of the type in which successive operations of a plunger alternately index a movable member from one position to another. The disclosed mechanism is particularly well adapted to alternately operating electrical switches.
It is well known to equip electrical switches and similar devices with push button actuators. Such actuators may be fabricated as part of the switches, or may be separately fabricated and combined with one or more switches. It is also well known to utilize push button actuators which, on successive depressions, cause switch contacts to alternately engage and disengage. For various applications it is required or desirable that push button actuators exhibit small button travel. It is also required in some applications that such actuators provide high tactile feedback.
Push button actuators which provide for alternate switch action are generally one of two types. In one type, means is provided for latching a push button actuator in a retracted position on alternate depressions. In its retracted position, the actuator is effective to either make or break a circuit. In the other type, successive strokes of the actuator alternately index a movable carrier from one position to another so as to provide for alternately engaging and disengaging contacts in one or more contact pairs.
A variety of constructions embodying the last described concept are known. Representative examples are disclosed in the following patents.
______________________________________ Patent No. Date Inventor ______________________________________ 436,412 (US) 09/16/1890 F. Goold 2,469,337 (US) 05/03/1949 E. Kohl 3,277,264 (US) 06/12/1962 R. Larkin 3,586,806 (US) 06/22/1971 W. Swisher 4,095,070 (US) 06/13/1978 K. Simpson 1,233,571 (GB) 05/26/1971 B. Baumanis ______________________________________
The implementations disclosed in U.S. Pat. Nos. 436,412, 3,277,264 and 4,095,070 and British patent 1,233,571, each use a pivoting carrier or member rotatable about a rivet, screw, stub shaft or yoke. In each case the pivot axis is fixed with respect to the switch housing. The pivoting carrier has a surface thereon configured with a pair of notches for receiving the free end of a deflectable plunger. The notches are located on opposite sides of a line joining the constrained end of the plunger and the pivot axis, and a ridge between the notches causes the free end of the plunger to slide into one or the other of the notches depending on the position of the carrier so that each depression of the plunger causes the carrier to change position.
The switch of U.S. Pat. No. 2,469,337 employs a movable contact or bridging element in the shape of a shallow V, the exterior of whose apex is configured and positioned to roll on a fixed center contact surface. A carriage assembly comprising a compression spring with a roller at one end and a notched abutment or block at the other is located between the bridging element and a transverse stationary rod. The roller is adapted to roll across the interior apex of the bridging element from one leg thereof to the other depending on the angular orientation of the center line of the spring relative to a line joining the center contact and the stationary rod.
The limiting positions of contact between the roller and the bridging element, and, therefore, the location and direction of force applied to the bridging element at the initiation of any switching action, are established by flanges on the bridging element which engage the roller. The location at which force is applied to the bridging element at the initiation of any switching action is substantially outside the limiting positions of the line of rolling contact between the bridging element and the fixed center contact surface.
Two of the notches on the block cooperate with the transverse rod to produce two normally stable positions for the carriage assembly in which the center line of the spring is in opposite angular orientations relative to the line joining the center contact and the rod. Two additional notches on the block cooperate with a pair of depending prongs on the bottom of a push button actuator to cause the carriage assembly to shift between stable positions upon successive depressions of the actuator.
In the switch of U.S. Pat. No. 3,586,806, an actuator assembly is coupled by means of a stud and yoke arrangement to a contact carrier which moves transversely to the direction of travel of a push button. An indexing slide, which forms part of the actuator assembly, is configured with a pair of tongues which alternately engage barbs on the push button so as to cause the assembly and slide therein to change position upon release of the push button.
All of these actuator designs require relatively large travel of the plunger or push button to achieve switching. In the implementations of U.S. Pat. Nos. 436,412, 3,277,264 and, 4,095,070 and British patent 1,233,571, large travel is dictated by the fixed relationship between the pivot axis and the line of action of the constrained end of the plunger. Because of this relationship, upon depression of the plunger, its free end must first slide along an incline into the valley of a notch before it can move the carrier. Lateral movement of the free end of the plunger is required to provide a moment arm through which force on the pivoting carrier can be transformed into a torque. The initial movement of the plunger has no effect on the position of the carrier. In addition, the effective length of the moment arm increases substantially as the pivoting carrier is rotated, thus requiring increased movement of the plunger during the actuation process.
In the switch apparatus of U.S. Pat. No. 2,469,337, one extreme position of the push button actuator is dictated by the requirement that the prongs thereon clear the ridges bounding notches on the notched block when the carrier assembly is oriented so that the ridges are in their highest positions. During actuation, the push button must first be depressed sufficiently to bring one prong into contact with the bottom of its associated notch, and further depressed sufficiently to cause the ridge between the notches which cooperate with the transverse rod to slip under the rod so that angular orientation of the carriage assembly may be changed. Such operation involves significant lost motion between the push button and the bridging element, and hence, relatively large push button travel.
In the case of U.S. Pat. No. 3,586,806, the requirement for relatively large push button travel is dictated by the fact that the push button must first be depressed sufficiently so that a barb thereon engages a tongue on a slide in the actuator assembly when the actuator assembly is in the position that the tongue is at its greatest distance from the rest position of the push button. The actuator assembly is then pulled by the push button to an overcenter position from which it snaps to an alternate stable position.
The applicant has devised a unique mechanism in which alternate action is achieved upon depression of a plunger with very small plunger travel. A moment arm is provided without requiring initial movement of the plunger and a minimum length lever arm is maintained throughout the actuation process. The mechanism design also provides for exceptionally high tactile feedback.